Slate does not work in Firefox Iframes

[maclockard]

Description

When rendering a slate editor inside of an Iframe using firefox, the editor does not render the initial content and is not intractable. There are no errors in the console AFAIK.

Possibly related to #4170?

Recording

Firefox is on the left, chrome is on the right:

Screen.Recording.2021-05-24.at.11.02.22.AM.mov

Sandbox

This repros in the official slate examples: https://www.slatejs.org/examples/iframe

Steps
To reproduce the behavior:

1. Go to https://www.slatejs.org/examples/iframe in Firefox
2. Try to use the editor

You will see that the editor does not render the initial text and that you can't interact with it.

Expectation

The editor renders the initial content and is intractable in Firefox. This currently works in Chrome.

Environment

• Slate Version: 0.63.0
• Operating System: macOS
• Browser: Firefox 88.0.1

[ottworks]

You can get the editor to work by opening the side menu and closing it again.